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Old 10-05-2011, 12:02   #1
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Loose Propeller Shaft Strut

My Southern Cross 39 has an external strut that holds the cutlass bearing (10 - 12" from hull) for the propeller shaft. The strut has developed a little side play, perhaps 1/4". The engine runs well and there is no vibration. The cutlass is not worn. It may have been this way for some time.

I am not sure how this is installed, but I have the impression that it is glassed in and the glass is probably working loose. My question is how serious is 1/4" side play in the strut and how immanently do I need to address it?
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Old 10-05-2011, 12:14   #2
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Re: Loose Propeller Shaft Strut

I would say it should be looked at promptly. Strut failure while underway could be catastrophic; at any rate side play in the strut would have a deleterious effect in the long run on your stuffing box.
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Old 10-05-2011, 12:45   #3
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Re: Loose Propeller Shaft Strut

Look at www.goodoldboat.com/pdfs/CutlessBearingsMay2002.pdf.
Lots of good info there.

Gordon
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Old 10-05-2011, 12:53   #4
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Re: Loose Propeller Shaft Strut

These struts / P-brackets are usually bedded and through-bolted with a hefty backing plate on the inside of the hull. The outside of the hull may be faired into the strut base. If properly sized and installed, the strut itself should never loosen and never exhibit any noticeable play.

Do you have access to the inside of the hull above the strut? If you can reach it from the inside (often difficult or impossible), you should be able to loosen the bolts and remove the strut. The odds are pretty good that at least a couple of them are loose or corroded.

If it doesn't get fixed... well, sudden catastrophic failure is, indeed, as bad as it sounds. Best case, you'd notice in time to kill the engine; worst case, the prop could come up through the bottom.
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Old 10-05-2011, 14:34   #5
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Re: Loose Propeller Shaft Strut

Another useful site:

P-bracket

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Old 10-05-2011, 15:00   #6
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Re: Loose Propeller Shaft Strut

don't ignore it fix asap. it will also allow water to enter boat around bolts. when we bought our boat there was no sign of a problem. we put her in and in the fall pulled out, but could not find out why bilge pump came on some what regularly. after haul out i noticed paint missing around strut mount location (boat was bottom painted by previous owner prior to purchase, yard did all the work ) anyway found the backing plate and bolts after becoming a contortion artist and with a mirror and light saw the reason the bolts and nuts were corroded. when i pulled strut the bearing was shot. must have been loose for some time before we bought.
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Old 10-05-2011, 15:19   #7
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Re: Loose Propeller Shaft Strut

I'd agree with everyone above. It's kind of like saying the thru-hull only has a little bit of play. I was taught that the prop shaft should have no more than about 1/8 in of play inside the cutlass bearing but now you have twice that. I'm totally surprised there are no other symptoms in terms of noise or vibration. I'd really expect the cutlass bearing is shot too. Hopefully, the prop shaft hasn't been to badly damaged but I wouldn't count on it.

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Old 10-05-2011, 17:00   #8
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Re: Loose Propeller Shaft Strut

Thanks for all the info. We are going to arrange to be hauled tomorrow. I will update in a few days when we have checked it out.
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Old 17-05-2011, 05:43   #9
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Re: Loose Propeller Shaft Strut

Hauled the boat. There was about 1/8 inch of side play. The strut mounting is covered in glass which may be fairing, but I think the strut is glassed in rather than bolted. It has worked some over the years. One side of the vertical part of the strut had little glass and the movement was to that side. I debated about tearing it out to completely redo it, but opted to more thoroughly glass the strut. I may have to redo with bolts some day, but tearing it out would take some time and I would prefer to do that in the winter, rather than during a cruise.

Used biaxial cloth from the strut onto the hull with West System on the weak side and wrapped both sides with finish cloth. Faired the whole thing and it is hard as a rock. Got a lot of advice from the yard and other boaters who looked at it. Feeling confident about it. Cutless bearing and engine alignment are good.

Thanks for all the help. I know some will disagree with the patch approach, but the posts encouraged me to go ahead with the haul.
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